This invention relates generally to electrical apparatus, and more particularly to high-current sliding contact assemblies.
Many devices used in the transmission and distribution of electrical energy require sliding contact current transfer members. Such devices include gas-insulated or air-type disconnect switches, grounding switches, high-current bus switches, and air- or gas-insulated transmission line joints. Each of these devices includes two electrical conductors which are relatively movable with respect to each other. In the case of the switches, the two conductors are relatively movable with respect to each other between an open position where the members are physically separated and a closed position wherein the members are in mechanical engagement allowing electrical energy to flow therebetween. In the case of air- or gas-insulated transmission line joints, the two members are movable with respect to one another to allow for thermal expansion of the conductors due to the heat generated in the transmission of the electrical energy.
The problem to be solved in all of these devices is that of reducing electrical resistance at the point of mechanical engagement. This resistance produces a joule-heating effect as current passes therethrough, thereby limiting the maximum amount of current which can be safely transferred. Methods for reducing this resistance include providing a large number of separate points of engagement between the separable members and providing contact pressure urging the two members together. While increasing the contact pressure and increasing the number of points of engagement between the separable members reduces the resistance, it also means that the forces required for moving the conductors relative to one another must be considerable, thereby either increasing the cost of such movement-imparting mechanism or incorporating other means for compensating for thermal expansion.
Prior art devices have included a plurality of spring-loaded contact fingers to provide a multiplicity of contact points upon each of which is exerted a spring force in a direction perpendicular to the direction of relative movement between the electrical conductors.
One problem with the prior art devices is the need to provide for misalignment of the two electrical conductors. This is especially critical for air- or gas-insulated transmission line joints, where each section of the line may be up to 60 feet in length and the maneuverability of such sections to provide for precise alignment is minimal.